To analyze changes in the chemical state of polymer materials caused by deterioration, the following methods are commonly employed: infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and the like. Though FT-IR or NMR allows detailed analysis of the chemical state, the information obtained is bulk information, and therefore it is difficult to analyze in detail the chemical state after deterioration which starts at a sample surface.
On the other hand, XPS is a surface-sensitive technique and is thus thought to be effective for analysis of changes in chemical state caused by deterioration. However, polymer materials are generally prepared by blending multiple polymers. For example, in cases where a material contains at least two diene polymers, analyzing the deterioration of each rubber component is important. However, it is difficult to determine the degree of deterioration of each rubber component by analyzing the deterioration by XPS.
Specifically, as shown in the results of XPS measurement performed on isoprene (IR) and butadiene (BR) in FIG. 1-1, chemical shifts of peaks do not occur in the XPS measurement even when different polymer species are used. Accordingly, it is difficult to analyze in detail the deterioration of each rubber component in a rubber blend.
Moreover, in diene polymers, since C═C (double bond) is generally considered to be cleaved due to deterioration, it is important to detect that bond. However, the peak of a C═C bond (double bond) and the peak of a C—C bond (single bond) overlap with each other at around 285 eV, and therefore the decrease in C═C bonds cannot be determined. Furthermore, diene polymers are known to be deteriorated by oxygen and ozone. The peak of oxygen deterioration and the peak of ozone deterioration also overlap with each other, and it is thus difficult to analyze them individually.
Meanwhile, to analyze changes in the chemical state of polymer materials, such as sulfur cross-linked diene rubbers, caused by deterioration, the following methods are commonly employed: physical property tests such as swell test, infrared spectroscopy (FT-IR) and the like.
In the swell test, a sample of a cross-linked polymer material is swelled with a low-molecular-weight solvent such as toluene to determine the network chain density. This method allows analysis of the cleavage and the recombination of rubber molecules before and after deterioration. However, since this method focuses on overall changes, it cannot be used to determine, for example, which is more deteriorated in a sulfur cross-linked polymer material, polymers or sulfur crosslinks. Moreover, in the FT-IR technique, functional groups generated by deterioration, such as C═O and OH, can be detected; however, this technique has low sensitivity to a S—S bond, and thus it cannot be used to determine which is deteriorated as in the case mentioned above.
Furthermore, it is considered that, if the degrees of deterioration of polymers and sulfur crosslinks can be determined individually in the analysis of the deterioration of a polymer material, then more effective measures against deterioration can be taken than conventional measures. The conventional methods as mentioned above also cannot analyze the deterioration ratio between polymers and sulfur crosslinks.
Meanwhile, as disclosed in Non-Patent Literatures 1 to 3, x-ray absorption spectra of polymers have been measured. None of literatures including the above literatures, however, teaches that the deterioration of each polymer in a polymer blend can be detected. Moreover, no document teaches that the oxygen deterioration and the ozone deterioration, into which the deterioration is divided, can be analyzed individually. Furthermore, there is no document relating to distinguishing deterioration factors using x-ray absorption spectra, or even relating to performing deterioration analysis by combining x-ray absorption spectra and X-ray photoelectron spectroscopy.